This invention pertains to lubricants and, more particularly, to a lubricating grease which is particularly useful for drive joints of front-wheel drive vehicles.
In front-wheel drive automobiles, vans, and trucks, the front wheels are driven by the engine via a front axle assembly and a number of front-wheel drive joints. These front-wheel drive joints facilitate movement of the front axle assembly while maintaining constant rotational velocity between the front wheels. The front-wheel drive joint is often referred to as a constant velocity (CV) joint. The outer CV joints usually have a protective boot comprising an elastomer, such as polyester or neoprene, and the inner joints usually have a protective boot comprising a higher temperature-resistant elastomer, such as silicon-based elastomers.
Front-wheel drive joints experience extreme pressures, torques, and loads during use. Operating temperatures can vary from -40.degree. F. during winter to over 300.degree. F. during summer.
Front-wheel drive greases are required to provide wear resistance. When a front-wheel drive vehicle is driven, sliding, rotational, and oscillatory (fretting) motions simultaneously occur within the front wheel drive joint, along with large loads and torques. A grease which minimizes wear from one of these motions or conditions will not necessarily protect against the others.
Front-wheel drive greases are also required to be chemically compatible with the elastomers and seals in front-wheel drive joints. Such greases should not chemically corrode, deform, or degrade the elastomers and seals which could cause swelling, hardening, loss of tensile strength, and ultimately rupture, oil leakage, and mechanical failure of the CV joints and seals.
Over the years, a variety of greases have been suggested for use with front-wheel drive joints and/or other mechanisms. Typifying such greases are those found in U.S. Pat. Nos. 2,964,475, 2,967,151, 3,344,065, 3,843,528, 3,846,314, 3,920,571, 4,107,058, 4,305,831, 4,431,552, 4,440,658, 4,514,312, and Re. 31,611. These greases have met with varying degrees of success.
It is, therefore, desirable to provide an improved front-wheel drive grease which overcomes most, if not all, of the above problems.